Sun's Sibling Stars Could Host Cousins of Earth Life

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Some scientists are searching not just for any life out there in
the universe, but for our distant relatives.

Earth may have seeded life on other planets if an asteroid
smacking into Earth sprayed DNA into space, researchers suggest.
Now a team of researchers is searching for siblings
of the sun — stars born from the same parent star cluster —
whose planets could have been impregnated with Earth life this
way.

The sun's birth cluster

The
sun is thought to have formed around 4.5 billion years ago
within a cluster of thousands of baby stars. After around 1
billion years, this cluster broke up and the sibling stars went
their separate ways. But before that point, researchers say, some
of these stars may have shared life in the form of
bacteria or DNA molecules.

"The idea is if a planet has life, like Earth, and if you hit it
with an asteroid, it will create debris, some of which will
escape into space," said astronomer Mauri Valtonen of the
University of Turku in Finland. "And if the debris is big enough,
like 1 meter across, it can shield life inside from radiation,
and that life can survive inside for millions of years until that
debris lands somewhere. If it happens to land on a planet with
suitable conditions, life can start there." [ Gallery:
The Smallest Alien Planets ]

That means that somewhere out there in the galaxy might be your
long-lost cousin.

If such a process ever happened, it was probably while the sun
was still in its birth cluster, near enough to other stars that
the chances were not negligible that debris bearing samples of
Earth microorganisms might smash into another planet.

During the time of the birth cluster, objects in the solar system
were under heavy bombardment by comets and asteroids, so
researchers say material could have been fairly easily
transferred between planets.

Research suggests it's equally possible that Earth itself was
seeded with life in such a manner, though neither scenario is
considered likely.

Searching for siblings

To pursue the idea, Valtonen is searching for these sibling stars
of the sun.

In a recent study, he analyzed a catalog called HIPPARCOS that
recorded the positions and motions of more than 100,000 stars.
Picking out those stars with radial velocities known to be
similar to the sun's, Valtonen and his colleagues identified two
promising stars, called HIP 87382 and HIP 47399, that also had
the same metal content and were at the same evolutionary stage as
the sun. According to the researchers' analysis, there are a few
percentage points of probability that these two were born in the
same cluster as our sun. Both are about 100 light-years from
Earth now.

Valtonen said the next step would be to search for planets around
these candidate stars.

"If we find an Earth-type planet, then it'd be a nice target for
this new generation of detectors to point at the atmosphere of
the planet," Valtonen told SPACE.com. "If there's a planet and it
has signs of life, then we could say perhaps they are relatives
in some sense."

You can follow SPACE.com assistant managing editor Clara
Moskowitz on Twitter@ClaraMoskowitz.
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